Non-removably mounted particulate and gaseous filter media have been housed in more or less conventional permanent frame constructions for many, many years. Such frames generally consist of metal channel members forming the four sides of a rectangular configuration with the edges of the filter media being disposed within the channels. Typically the side walls of the channel members are bent inwardly to firmly engage and fix the outer edges of a layer of filter media in position within the frame.
While this is generally a satisfactory construction for particulate filter media of relatively long life or which can be cleaned and re-used, it represents a considerable expense in those applications wherein the filter media is relatively short-lived. In such situations, a disposable and replaceable media is desirable.
In applications wherein a combination of particulate and gaseous filter media are required, it is not unusual for one or more types of such media to be relatively shortlived. In this situation, a less expensive disposable filter media held by an inexpensive throwaway frame construction is desirable.
However, prior frame constructions of the stronger permanent type do not readily permit removal and replacement of layers of filter media held therein and the less expensive disposable frame constructions are less sturdy, weak and otherwise not satisfactory for certain applications. The prior art has incorporated all filter media within a singular frame which must be thrown away when one or more of the filter media has served its useful life or to employ a separate filter frame for each type of media used.
In certain applications, it is desirable to provide multiple filter media in a given application wherein one of the media types are preferably disposable. Prior to the present invention a suitable frame construction which combines the desirable characteristics of a conventional strong metal frame with the desirability of employing one or more disposable layers of filter media has not been satisfactorily provided by those skilled in the art.